A full-wave rectifying circuit is typically used to obtain a DC voltage from a single-phase AC voltage input from a single-phase AC power supply. An output from the full-wave rectifying circuit, however, has power pulsations having a frequency twice the frequency of the single-phase AC voltage. To reduce the power pulsations, a power buffer circuit for buffering a power is thus required between an output of the full-wave rectifying circuit and a load. A capacitive element, for example, referred to as a smoothing capacitor is required for buffering a power.
Irie, Yamashita, and Takemoto, “Ripple Compensation for a Single-Phase Rectifier by 2-Quadrant Chopper and Auxiliary Capacitor”, the Institute of Electrical Engineers of Japan (IEEJ) Transactions D, Vol. 112, No. 7, pp. 623-629 (1992) discloses a technique for connecting a buffer capacitor to a smoothing capacitor via a current-reversible chopper to absorb a pulsating power. This technique reduces the electrostatic capacitance of the smoothing capacitor and further allows voltage ripples at the buffer side to greatly reduce the total electrostatic capacitance required for smoothing.
Ohnuma, Itoh, “Circuit Configuration and Control Strategy of single-to-three Phase Power Converter with Active Buffer and Charge Circuit”, the 2010 Annual Meeting of IEEJ, 4-057 (2010) and Japanese Patent Application Laid-Open No. 2011-193678 disclose a technique for connecting a buffer capacitor to a DC link via a switching element while removing the smoothing capacitor of Irie, Yamashita, and Takemoto, “Ripple Compensation for a Single-Phase Rectifier by 2-Quadrant Chopper and Auxiliary Capacitor”, the Institute of Electrical Engineers of Japan (IEEJ) Transactions D, Vol. 112, No. 7, pp. 623-629 (1992). A direct conversion circuit is described that generates a voltage source by this technique and generates a high-frequency link along with a power supply voltage.
Ohnuma, Itoh, “Comparison between a Boost Chopper and an Active Buffer as a Single to Three Phase Converter”, 2011 Annual Meeting of IEEJ, 4-042 (2011) further discloses a technique for converting an input waveform into a sinusoidal waveform and increasing efficiency.
The techniques described in Ohnuma, Itoh, “Circuit Configuration and Control Strategy of single-to-three Phase Power Converter with Active Buffer and Charge Circuit”, the 2010 Annual Meeting of IEEJ, 4-057 (2010) and Ohnuma, Itoh, “Comparison between a Boost Chopper and an Active Buffer as a Single to Three Phase Converter”, 2011 Annual Meeting of IEEJ, 4-042 (2011) improve a voltage utilization ratio (a ratio of a voltage across a DC link to a crest value of a power supply voltage) from 0.5 to 1/√2=0.71, compared with the conventionally proposed technique involving the use of an active snubber (for example, see Ohnuma, Itoh, “Control Strategy of Single Phase to Three Phase Power Converter Using an Active Snubber”, 2008 IEEJ Industry Applications Society Conference, 1-20 (2008)). However, the voltage across the DC link is low compared with a typical single-phase rectifier. This may increase the current capacity of a power device of an inverter.
To solve the problem above, Japanese Patent No. 5454732 proposes a technique for controlling the voltage across a DC link to have a waveform obtained by full-wave rectification of a two-phase AC and setting an average voltage utilization ratio to 0.9 at maximum.
As described above, the techniques proposed in Ohnuma, Itoh, “Circuit Configuration and Control Strategy of single-to-three Phase Power Converter with Active Buffer and Charge Circuit”, the 2010 Annual Meeting of IEEJ, 4-057 (2010), Ohnuma, Itoh, “Comparison between a Boost Chopper and an Active Buffer as a Single to Three Phase Converter”, 2011 Annual Meeting of IEEJ, 4-042 (2011), Japanese Patent Application Laid-Open No. 2011-193678 and Japanese Patent No. 5454732, which are based on the concept of a power flow, buffer the power pulsations by a power buffer circuit to supply a steady power to an inverter.